Terminal device and method for facilitating communication between terminal devices

ABSTRACT

A method in a first terminal device for facilitating direct communication with a second terminal device. The method comprises transmitting to the second terminal device a Modulation and Coding Scheme (MCS) index, based on which the second terminal device can obtain a modulation order and a Transport Block Size (TBS) in accordance with a first mapping or a second mapping between MCS indices on one hand and modulation orders and TBSs on the other. The MCS index is determined by the first terminal device by selectively applying the first or second mapping.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 16/496,938,filed Sep. 23, 2019, which is a National stage of InternationalApplication No. PCT/CN2018/080203, filed Mar. 23, 2018, which claimspriority to International Application No. PCT/CN2017/078070, filed Mar.24, 2017, which are all hereby incorporated by reference.

TECHNICAL FIELD

The present disclosure relates to communication technology, and moreparticularly, to a terminal device and a method for facilitating directcommunication between terminal devices.

BACKGROUND

Vehicle to Vehicle/Pedestrian/Infrastructure/Network (V2X) has beenstandardized in Long Term Evolution (LTE) Release 14. According to theRelease 14 standard, only Quadrature Phase Shift Keying (QPSK) and 16Quadrature Amplitude Modulation (QAM) are supported for sidelinkcommunications. In RAN#75 meeting, a new work item for V2X was approvedin RP-170798, New WID on 3GPP V2X Phase 2, 3GPP, March 2017. One of theobjectives in this work item is introduction of 64 QAM. That is, Release15 V2X terminals are required to support 64 QAM.

In the Release 14 V2X, modulation orders and Transport Block Size (TBS)indices are determined from a “Modulation and Coding Scheme (MCS)” fieldin a Sidelink Control Information (SCI) format. The MCS field containsan MCS index, based on which the corresponding modulation order and TBScan be obtained. The scheme for determining modulation orders and TBSsfor Physical Uplink Shared Channel (PUSCH) in the LTE is reused inPhysical Sidelink Shared Channel (PSSCH). Table 1 below shows a mappingfrom MCS indices (I_(MCS)) to modulation orders (Q′_(m)) and TB Sindices (I_(TBS)) in the Release 14 V2X.

TABLE 1 Mapping from I_(MCS) to Q′_(m) and I_(TBS) for Release 14 V2XMCS Index Modulation Order TBS Index Coding Rate I_(MCS) Q′_(m) I_(TBS)(no retransmission) 0 2 0 0.10 1 2 1 0.15 2 2 2 0.25 3 2 3 0.31 4 2 40.36 5 2 5 0.39 6 2 6 0.44 7 2 7 0.57 8 2 8 0.68 9 2 9 0.79 10 2 10 0.4411 4 10 0.88 12 4 11 0.51 13 4 12 0.59 14 4 13 0.65 15 4 14 0.73 16 4 150.78 17 4 16 0.84 18 4 17 0.92 19 4 18 1.01 20 4 19 1.12 21 4 19 1.12 224 20 1.20 23 4 21 1.28 24 4 22 1.40 25 4 23 1.51 26 4 24 1.56 27 4 251.62 28 4 26 1.92 29 Reserved 30 31

Table 1 also shows coding rates corresponding to the modulation ordersand TBS indices, with no retransmission assumed. Theoretically, a codingrate higher than one would render a transport block not decodable by areceiver. In practice, a transport block having a coding rate higherthan a smaller threshold, e.g., 0.93 as discussed in Release 8, wouldnot be decodable. In either criterion, it can be seen from Table 1 that,for 19≤I_(MCS)≤28, the coding rates are too high to be decodable at areceiver. In other words, the above Release 14 mapping does not“support” those MCSs in the sense that they are not decodable.

In order to introduce 64 QAM, a straightforward way is to reuse themapping for PUSCH in LTE, as shown in Table 2 below.

TABLE 2 Mapping from I_(MCS) to Q′_(m) and I_(TBS) for PUSCH MCS IndexModulation Order TBS Index Coding Rate I_(MCS) Q′_(m) I_(TBS) (noretransmission) 0 2 0 0.10 1 2 1 0.15 2 2 2 0.25 3 2 3 0.31 4 2 4 0.36 52 5 0.39 6 2 6 0.44 7 2 7 0.57 8 2 8 0.68 9 2 9 0.79 10 2 10 0.44 11 410 0.88 12 4 11 0.51 13 4 12 0.59 14 4 13 0.65 15 4 14 0.73 16 4 15 0.7817 4 16 0.84 18 4 17 0.92 19 4 18 1.01 20 4 19 1.12 21 6 19 0.75 22 6 200.80 23 6 21 0.85 24 6 22 0.93 25 6 23 1.01 26 6 24 1.04 27 6 25 1.08 286 26 1.28 29 Reserved 30 31 Note: One OFDM symbol is used for theAutomatic Gain Control (AGC) settling for QPSK and two for 16QAM/64QAM.

However, as can be seen in Table 2, even with the introduction of 64QAM, for 25≤I_(MCS)≤28, the coding rates are still too high to bedecodable, which would be inefficient for 64 QAM transmissions.

Meanwhile, it is desired that Release 15 V2X terminals should bebackward compatible. That is, Release 15 V2X terminals shall co-existwith Release 14 V2X terminals in the same resource pools and use thesame scheduling assignment format (which can be decoded by legacyterminals). Eventually, the Release 14 and Release 15 V2X terminalsshall be able to communicate with each other directly over sidelink,which requires the Release 14 V2X terminals to be able to decode PSSCHtransmitted from the Release 15 V2X terminals, and vice versa.

SUMMARY

It is an object of the present disclosure to provide a terminal deviceand a method for facilitating direct communication between terminaldevices, capable of solving at least one of the above problems.

According to a first aspect of the present disclosure, a method in afirst terminal device for facilitating direct communication with asecond terminal device is provided. The method comprises: transmittingto the second terminal device a Modulation and Coding Scheme (MCS)index, based on which the second terminal device can obtain a modulationorder and a Transport Block Size (TBS) in accordance with a firstmapping or a second mapping between MCS indices on one hand andmodulation orders and TBSs on the other. The MCS index is determined bythe first terminal device by selectively applying the first or secondmapping.

In an embodiment, the second mapping supports a higher modulation orderthan those supported by the first mapping.

In an embodiment, the first and second mappings have an overlappedportion.

In an embodiment, the overlapped portion is associated with one or moreof modulation orders supported by both the first and second mappings.

In an embodiment, the overlapped portion is associated with coding ratesbelow a predefined threshold.

In an embodiment, in a portion of the second mapping that does notoverlap the first mapping, each TBS associated with the second mappingis scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements,REs, available for data transmission.

In an embodiment, the MCS index is determined by the first terminaldevice by applying the first mapping when retransmission is configured,or the second mapping when no retransmission is configured and amodulation order and a TBS obtained by applying the first mapping wouldresult in a coding rate higher than a predefined threshold.

In an embodiment, the method further comprises: transmitting to thesecond terminal device an indicator indicating which of the first andsecond mappings is applied by the first terminal device.

In an embodiment, the second terminal device supports the first mappingonly.

In an embodiment, the first and second terminal devices arecommunicating directly with each other on a sidelink for vehicularservices.

According to a second aspect of the present disclosure, a method in afirst terminal device for facilitating direct communication with asecond terminal device is provided. The method comprises: receiving fromthe second terminal device a Modulation and Coding Scheme (MCS) indexdetermined by the second terminal device by applying a first mapping ora second mapping between MCS indices on one hand and modulation ordersand Transport Block Sizes (TBSs) on the other; and obtaining, based onthe MCS index, a modulation order and a TBS selectively in accordancewith the first or second mapping.

In an embodiment, the second mapping supports a higher modulation orderthan those supported by the first mapping.

In an embodiment, the first and second mappings have an overlappedportion.

In an embodiment, the overlapped portion is associated with one or moreof modulation orders supported by both the first and second mappings.

In an embodiment, the overlapped portion is associated with coding ratesbelow a predefined threshold.

In an embodiment, in a portion of the second mapping that does notoverlap the first mapping, each TBS associated with the second mappingis scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements,REs, available for data transmission.

In an embodiment, the modulation order and the TBS are obtained by thefirst terminal device in accordance with the first mapping whenretransmission is configured, or with the second mapping when noretransmission is configured and a modulation order and a TBS obtainedin accordance with the first mapping would result in a coding ratehigher than a predefined threshold.

In an embodiment, the method further comprises: receiving from thesecond terminal device an indicator indicating which of the first andsecond mappings is applied by the second terminal device.

In an embodiment, the second terminal device supports the first mappingonly.

In an embodiment, the first and second terminal devices arecommunicating directly with each other on a sidelink for vehicularservices.

According to a third aspect of the present disclosure, a first terminaldevice in direct communication with a second terminal device isprovided. The first terminal device comprises a transceiver, a processorand a memory. The memory comprises instructions executable by theprocessor whereby the first terminal device is operative to perform themethod according to the above first or second aspect.

According to a fourth aspect of the present disclosure, a computerreadable storage medium is provided. The computer readable storagemedium has computer program instructions stored thereon. The computerprogram instructions, when executed by a processor in a first terminaldevice, cause the first terminal device to perform the method accordingto the above first or second aspect.

With the embodiments of the present disclosure, two mappings between MCSindices on one hand and modulation orders and TBSs on the other areprovided. A terminal device supporting both mappings can selectivelyapply one of the two mappings, so as to communicate with anotherterminal device that may support only one mapping. Further, one of thetwo mappings can be designed to provide higher modulation orders andthus lower but decodable coding rates than the other. In this way, theMCSs can be more efficient.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages will be moreapparent from the following description of embodiments with reference tothe figures, in which:

FIG. 1 is a flowchart illustrating a method for facilitating directcommunication between terminals according to an embodiment of thepresent disclosure;

FIG. 2 is a flowchart illustrating a method for facilitating directcommunication between terminals according to another embodiment of thepresent disclosure;

FIG. 3 is a block diagram of a terminal device according to anembodiment of the present disclosure;

FIG. 4 is a block diagram of a terminal device according to anotherembodiment of the present disclosure; and

FIG. 5 is a block diagram of a terminal device according to yet anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

The embodiments of the disclosure will be detailed below with referenceto the drawings. It should be appreciated that the following embodimentsare illustrative only, rather than limiting the scope of the disclosure.

It shall be understood that although the terms “first” and “second” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are only used to distinguishone element from another. For example, a first element could be termed asecond element, and similarly, a second element could be termed a firstelement, without departing from the scope of example embodiments. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed terms.

FIG. 1 is a flowchart illustrating a method 100 for facilitating directcommunication between terminal devices according to an embodiment of thepresent disclosure. The method 100 can be performed at a first terminaldevice in direct communication with a second terminal device. The firstand second terminal devices can communicate directly with each other ona sidelink for vehicular services. For example, the first terminaldevice can be a Release 15 V2X terminal as described above and thesecond terminal device can be a Release 14 or Release 15 V2X terminal.

It can be appreciated by those skilled in the art that the concept ofthe present disclosure is not limited to Release 14 or Release 15 V2Xterminals, but applies generally to scenarios in which new and legacyterminals having different MCSs are in communication with each other.The method 100 includes the following step.

At step S110, an MCS index is transmitted to the second terminal device.Based on the MCS index, the second terminal device can obtain amodulation order and a TBS in accordance with a first mapping or asecond mapping between MCS indices on one hand and modulation orders andTBSs on the other. The MCS index is determined by the first terminaldevice by selectively applying the first or second mapping.

Table 3 below shows an example of mappings from MCS indices (I_(MCS)) tomodulation orders (Q′_(m)) and TBS indices (I_(TBS)). Table 4 showscorresponding mappings from TBS indices (I_(TBS)) to TBSs (in unit ofbits). That is, the mappings between MCS indices and modulation ordersare given by Table 3 alone, and the mappings between MCS indices andTBSs are given by Table 3 and Table 4 in combination. In other words,the first mapping described in the step S110 can be obtained from thesecond and third columns of Table 3 and the second column of Table 4,and the second mapping described in the step S110 can be obtained fromthe fourth and fifth columns of Table 3 and the third column of Table 4.In Table 4, the number of Physical Resource Blocks (PRBs), denoted as X,can be any valid number for allocated PRBs. Table 4 also shows codingrates of the first and second mappings.

TABLE 3 Mapping from I_(MCS) to Q′_(m) and I_(TBS) 1^(st) Mapping 2^(nd)Mapping MCS Modulation TBS Modulation TBS Index Order Index Order IndexI_(MCS) Q′_(m) I_(TBS) Q′_(m) I_(TBS) 0 2 0 2 0 1 2 1 2 1 2 2 2 2 2 3 23 2 3 4 2 4 2 4 5 2 5 2 5 6 2 6 2 6 7 2 7 2 7 8 2 8 2 8 9 2 9 2 9 10 210 2 10 11 4 10 4 10 12 4 11 4 11 13 4 12 4 12 14 4 13 4 13 15 4 14 4 1416 4 15 4 15 17 4 16 4 16 18 4 17 4 17 19 4 18 4 18 20 4 19 4 19 21 4 196 19 22 4 20 6 20 23 4 21 6 21 24 4 22 6 22 25 4 23 6 23 26 4 24 6 24 274 25 6 25 28 4 26 6 26 29 Reserved 30 31

TABLE 4 Mappings from TBS Indices to TBSs 1^(st) 2^(nd) Mapping Mapping1^(st) 2^(nd) PRB Mapping Mapping I_(TBS) X X Coding Rate Coding Rate 056 56 0.10 0.10 1 88 88 0.15 0.15 2 144 144 0.25 0.25 3 176 176 0.310.31 4 208 208 0.36 0.36 5 224 224 0.39 0.39 6 256 256 0.44 0.44 7 328328 0.57 0.57 8 392 392 0.68 0.68 9 456 456 0.79 0.79 10 504 504 0.440.44 11 584 584 0.51 0.51 12 680 680 0.59 0.59 13 744 744 0.65 0.65 14840 840 0.73 0.73 15 904 904 0.78 0.78 16 968 968 0.84 0.84 17 1064 10640.92 0.92 18 1160 1160 1.01 1.01 19 1288 752 1.12 0.65 20 1384 808 1.20.47 21 1480 864 1.28 0.50 22 1608 944 1.4 0.54 23 1736 1016 1.51 0.5924 1800 1056 1.56 0.61 25 1864 1088 1.62 0.63 26 2216 1296 1.92 0.75

In this example, the second mapping can support a higher modulationorder (e.g., 64 QAM) than those supported by the first mapping (e.g.,QPSK and 16 QAM).

Moreover, in this example, the first and second mappings have anoverlapped portion (0≤I_(MCS)≤20). The overlapped portion is associatedwith modulation orders supported by both the first and second mappings(i.e., QPSK and 16 QAM).

With the overlapped portion, even if the second terminal device supportsthe first mapping only and the first terminal device determines the MCSindex by applying the second mapping, the second terminal device canhave the same understanding of the modulation order and TBS as the firstterminal device as long as the determined MCS index is within theoverlapped portion.

In a portion of the second mapping that does not overlap the firstmapping (21≤I_(MCS)≤28), each TBS associated with the second mapping canbe scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements(REs) (or OFDM symbols) available for data transmission.

In this example, assuming that 12 OFDM symbols are available for datatransmission over PUSCH and 7 over PSSCH, the TBSs in the second mappingcan be scaled down by a factor of 7/12 with respect to those in thefirst mapping (19≤I_(TBS)≤26). As can be seen from Table 4, for thesecond mapping, the coding rates for 64 QAM (19≤I_(TBS)≤26) are lowerthan 0.93 and thus decodable.

Table 5 below shows another example of mappings from MCS indices(I_(MCS)) to modulation orders (Q′_(m)) and TBS indices (I_(TBS)). Table6 shows corresponding mappings from TBS indices (I_(TBS)) to TBSs (inunit of bits). Similarly, the first mapping described in the step S110can be obtained from the second and third columns of Table 5 and thesecond column of Table 6, and the second mapping described in the stepS110 can be obtained from the fourth and fifth columns of Table 5 andthe third column of Table 6.

TABLE 5 Mapping from I_(MCS) to Q′_(m) and I_(TBS) 1^(st) Mapping 2^(nd)Mapping MCS Modulation TBS Modulation TBS Index Order Index Order IndexI_(MCS) Q′_(m) I_(TBS) Q′_(m) I_(TBS) 0 2 0 2 0 1 2 1 2 1 2 2 2 2 2 3 23 2 3 4 2 4 2 4 5 2 5 2 5 6 2 6 2 6 7 2 7 2 7 8 2 8 2 8 9 2 9 2 9 10 210 2 10 11 4 10 4 10 12 4 11 4 11 13 4 12 4 12 14 4 13 4 13 15 4 14 4 1416 4 15 4 15 17 4 16 4 16 18 4 17 4 17 19 4 18 4 18 20 4 19 4 19 21 4 196 19 22 4 20 6 20 23 4 21 6 21 24 4 22 6 22 25 4 23 6 23 26 4 24 6 24 274 25 6 25 28 4 26 6 26 29 Reserved 30 31

TABLE 6 Mappings from TBS Indices to TBSs 1^(st) 2^(nd) Mapping Mapping1^(st) 2^(nd) PRB Mapping Mapping I_(TBS) X X Coding Rate Coding Rate 056 56 0.10 0.10 1 88 88 0.15 0.15 2 144 144 0.25 0.25 3 176 176 0.310.31 4 208 208 0.36 0.36 5 224 224 0.39 0.39 6 256 256 0.44 0.44 7 328328 0.57 0.57 8 392 392 0.68 0.68 9 456 456 0.79 0.79 10 504 504 0.440.44 11 584 584 0.51 0.51 12 680 680 0.59 0.59 13 744 744 0.65 0.65 14840 840 0.73 0.73 15 904 904 0.78 0.78 16 968 968 0.84 0.84 17 1064 10640.92 0.92 18 1160 680 1.01 0.59 19 1288 752 1.12 0.65 20 1384 808 1.20.47 21 1480 864 1.28 0.50 22 1608 944 1.4 0.54 23 1736 1016 1.51 0.5924 1800 1056 1.56 0.61 25 1864 1088 1.62 0.63 26 2216 1296 1.92 0.75

In the example shown in Table 5 and Table 6, the first and secondmappings have an overlapped portion (0≤I_(MCS)≤18). The overlappedportion is associated with coding rates below a predefined threshold(e.g., 0.93).

In the example shown in Table 5 and Table 6, in a portion of the secondmapping that does not overlap the first mapping (19≤I_(MCS)≤28), eachTBS associated with the second mapping can be scaled down with respectto a corresponding TBS associated with the first mapping by a factordependent on a number of Resource Elements (REs) (or OFDM symbols)available for data transmission. Again, the factor can be e.g., 7/12.

Table 7 below shows yet another example of mappings from MCS indices(I_(MCS)) to modulation orders (Q′_(m)) and TBS indices (I_(TBS)). Table8 shows corresponding mappings from TBS indices (I_(TBS)) to TBSs (inunit of bits). Similarly, the first mapping described in the step S110can be obtained from the second and third columns of Table 7 and thesecond column of Table 8, and the second mapping described in the stepS110 can be obtained from the fourth and fifth columns of Table 7 andthe third column of Table 8. Compared with the previous examples, herethe first and second mappings have a smaller overlapped portion(0≤I_(MCS)≤4).

TABLE 7 Mapping from I_(MCS) to Q′_(m) and I_(TBS) 1^(st) Mapping 2^(nd)Mapping MCS Modulation TBS Modulation TBS Index Order Index Order IndexI_(MCS) Q′_(m) I_(TBS) Q′_(m) I_(TBS) 0 2 0 2 0 1 2 1 2 1 2 2 2 2 2 3 23 2 3 4 2 4 2 4 5 2 5 4 5 6 2 6 4 6 7 2 7 4 7 8 2 8 4 8 9 2 9 4 9 10 210 6 10 11 4 10 6 10 12 4 11 6 11 13 4 12 6 12 14 4 13 6 13 15 4 14 6 1416 4 15 6 15 17 4 16 6 16 18 4 17 6 17 19 4 18 6 18 20 4 19 6 19 21 4 196 19 22 4 20 6 20 23 4 21 6 21 24 4 22 6 22 25 4 23 6 23 26 4 24 6 24 274 25 6 25 28 4 26 6 26 29 Reserved 30 31

TABLE 8 Mappings from TBS Indices to TBSs 1^(st) 2^(nd) Mapping Mapping1^(st) 2^(nd) PRB Mapping Mapping I_(TBS) X X Coding Rate Coding Rate 056 56 0.10 0.10 1 88 88 0.15 0.15 2 144 144 0.25 0.25 3 176 176 0.310.31 4 208 208 0.36 0.36 5 224 224 0.39 0.20 6 256 256 0.44 0.22 7 328328 0.57 0.29 8 392 392 0.68 0.34 9 456 456 0.79 0.40 10 504 504 0.440.15 11 584 584 0.51 0.34 12 680 680 0.59 0.39 13 744 744 0.65 0.43 14840 840 0.73 0.49 15 904 904 0.78 0.52 16 968 968 0.84 0.56 17 1064 10640.92 0.61 18 1160 680 1.01 0.39 19 1288 752 1.12 0.44 20 1384 808 1.20.47 21 1480 864 1.28 0.50 22 1608 944 1.4 0.54 23 1736 1016 1.51 0.5924 1800 1056 1.56 0.61 25 1864 1088 1.62 0.63 26 2216 1296 1.92 0.75

In the examples shown in Tables 3˜8, it is assumed that noretransmission is configured, as in Tables 1˜2. When retransmission isconfigured, e.g., when one retransmission is provided, Table 1 wouldbecome Table 9 below:

TABLE 9 Mapping from I_(MCS) to Q′_(m) and I_(TBS) with OneRetransmission MCS Index Modulation Order TBS Index Coding Rate I_(MCS)Q′_(m) I_(TBS) (1 retransmission) 0 2 0 0.05 1 2 1 0.08 2 2 2 0.13 3 2 30.16 4 2 4 0.18 5 2 5 0.20 6 2 6 0.22 7 2 7 0.29 8 2 8 0.34 9 2 9 0.4010 2 10 0.22 11 4 10 0.44 12 4 11 0.26 13 4 12 0.30 14 4 13 0.33 15 4 140.37 16 4 15 0.39 17 4 16 0.42 18 4 17 0.46 19 4 18 0.51 20 4 19 0.56 214 19 0.56 22 4 20 0.60 23 4 21 0.64 24 4 22 0.70 25 4 23 0.76 26 4 240.78 27 4 25 0.81 28 4 26 0.96 29 Reserved 30 31

As the corresponding mapping from TBS indices (I_(TBS)) to TBSs (in unitof bits), the second column of Table 4 or Table 6 can be reused. It canbe seen that, in Table 9, all the MCSs have coding rates lower than 0.93except for I_(MCS)=28. That is, almost all the MCSs are decodable withone retransmission.

According to 3GPP TS 36.212 v14.1.1 (2017-01), Section 5.4.3.1.2, theSCI also contains a retransmission index. A terminal device candetermine whether retransmission is configured based on this index.

Accordingly, in the step S110, the MCS index can be determined by thefirst terminal device by applying the first mapping when retransmissionis configured, or the second mapping when no retransmission isconfigured and a modulation order and a TBS obtained by applying thefirst mapping would result in a coding rate higher than a predefinedthreshold (e.g., 0.93). Here, the first mapping may include twoportions: a first portion in which each MCS index can be used regardlessof whether retransmission is configured, and a second portion in whicheach MCS index can only be used when retransmission is configured.Accordingly, the second mapping may be the first portion of the firstmapping. For example, the first mapping may include MCS indices 0˜28 inTable 9 (or a scaled down version thereof), while the second mapping mayinclude MCS indices 0˜27 in Table 9 (or the accordingly scaled downversion).

In an example, the method 100 may further include a step S120 in whichthe first terminal device transmits to the second terminal device anindicator indicating which of the first and second mappings is appliedby the first terminal device. In this way, for example, when the secondterminal device is a Release 15 V2X terminal, it can parse the MCS indexto obtain the modulation order and the TBS in accordance with the samemapping as applied by the first terminal device. On the other hand, ifthe second terminal device is e.g., a Release 14 V2X terminal thatcannot parse the indicator and/or cannot support the second mapping, itcan simply ignore and discard the indicator.

FIG. 2 is a flowchart illustrating a method 200 for facilitating directcommunication between terminals according to an embodiment of thepresent disclosure. The method 100 can be performed at a first terminaldevice in direct communication with a second terminal device. The firstand second terminal devices can communicate directly with each other ona sidelink for vehicular services. For example, the first terminaldevice can be a Release 15 V2X terminal as described above and thesecond terminal device can be a Release 14 or Release 15 V2X terminal.

At step S210, an MCS index is received from the second terminal device.The MCS index is determined by the second terminal device by applying afirst mapping or a second mapping between MCS indices on one hand andmodulation orders and TBSs on the other.

In an example, the second mapping can support a higher modulation order(e.g., 64 QAM) than those supported by the first mapping (e.g., QPSK and16 QAM).

In an example, the first and second mappings can have an overlappedportion. The overlapped portion can be associated with one or more ofmodulation orders supported by both the first and second mappings.Additionally or alternatively, the overlapped portion can be associatedwith coding rates below a predefined threshold (e.g., 0.93). In aportion of the second mapping that does not overlap the first mapping,each TBS associated with the second mapping is scaled down with respectto a corresponding TBS associated with the first mapping by a factordependent on a number of REs or OFDM symbols available for datatransmission.

At step S220, a modulation order and a TBS are obtained based on the MCSindex selectively in accordance with the first or second mapping.

In the step S220, the modulation order and the TBS can be obtained bythe first terminal device selectively in accordance with the firstmapping when retransmission is configured, or with the second mappingwhen no retransmission is configured and a modulation order and a TBSobtained in accordance with the first mapping would result in a codingrate higher than a predefined threshold (e.g., 0.93).

In an example, the second terminal device may support the first mappingonly.

In an example, the method 200 may further include a step S230 in whichthe first terminal device receives from the second terminal device anindicator indicating which of the first and second mappings is appliedby the second terminal device.

The examples described above in connection with FIG. 1 and the method100, especially those related to Tables 3˜9, are applicable to themethod 200.

Correspondingly to the method 100 as described above, a terminal deviceis provided. FIG. 3 is a block diagram of a first terminal device 300 indirect communication with a second terminal device according to anembodiment of the present disclosure.

As shown in FIG. 3, the terminal device 300 includes a communicationunit 310 configured to transmit to the second terminal device an MCSindex, based on which the second terminal device can obtain a modulationorder and a TBS in accordance with a first mapping or a second mappingbetween MCS indices on one hand and modulation orders and TBSs on theother. The MCS index is determined by the first terminal device byselectively applying the first or second mapping.

In an embodiment, the second mapping supports a higher modulation orderthan those supported by the first mapping.

In an embodiment, the first and second mappings have an overlappedportion.

In an embodiment, the overlapped portion is associated with one or moreof modulation orders supported by both the first and second mappings.

In an embodiment, the overlapped portion is associated with coding ratesbelow a predefined threshold.

In an embodiment, in a portion of the second mapping that does notoverlap the first mapping, each TBS associated with the second mappingis scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements,REs, available for data transmission.

In an embodiment, the MCS index is determined by the first terminaldevice by applying the first mapping when retransmission is configured,or the second mapping when no retransmission is configured and amodulation order and a TBS obtained by applying the first mapping wouldresult in a coding rate higher than a predefined threshold.

In an embodiment, the communication unit 310 is further configured totransmit to the second terminal device an indicator indicating which ofthe first and second mappings is applied by the first terminal device.

In an embodiment, the second terminal device supports the first mappingonly.

In an embodiment, the first and second terminal devices arecommunicating directly with each other on a sidelink for vehicularservices.

The above unit 310 can be implemented as a pure hardware solution or asa combination of software and hardware, e.g., by one or more of: aprocessor or a micro-processor and adequate software and memory forstoring of the software, a Programmable Logic Device (PLD) or otherelectronic component(s) or processing circuitry configured to performthe actions described above, and illustrated, e.g., in FIG. 1.

Correspondingly to the method 200 as described above, a terminal deviceis provided. FIG. 4 is a block diagram of a terminal device 400 (whichis referred to as the first terminal device hereafter) in directcommunication with a second terminal device according to anotherembodiment of the present disclosure.

As shown in FIG. 4, the terminal device 400 includes a communicationunit 410 configured to receive from the second terminal device an MCSindex determined by the second terminal device by applying a firstmapping or a second mapping between MCS indices on one hand andmodulation orders and TBSs on the other. The terminal device 400 furtherincludes an obtaining unit 420 configured to obtain, based on the MCSindex, a modulation order and a TBS selectively in accordance with thefirst or second mapping.

In an embodiment, the second mapping supports a higher modulation orderthan those supported by the first mapping.

In an embodiment, the first and second mappings have an overlappedportion.

In an embodiment, the overlapped portion is associated with one or moreof modulation orders supported by both the first and second mappings.

In an embodiment, the overlapped portion is associated with coding ratesbelow a predefined threshold.

In an embodiment, in a portion of the second mapping that does notoverlap the first mapping, each TBS associated with the second mappingis scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements,REs, available for data transmission.

In an embodiment, the modulation order and the TBS are obtained by thefirst terminal device selectively in accordance with the first mappingwhen retransmission is configured, or with the second mapping when noretransmission is configured and a modulation order and a TBS obtainedin accordance with the first mapping would result in a coding ratehigher than a predefined threshold.

In an embodiment, the communication unit 410 is further configured toreceive from the second terminal device an indicator indicating which ofthe first and second mappings is applied by the second terminal device.

In an embodiment, the second terminal device supports the first mappingonly.

In an embodiment, the first and second terminal devices arecommunicating directly with each other on a sidelink for vehicularservices.

The above units 410-420 can be implemented as a pure hardware solutionor as a combination of software and hardware, e.g., by one or more of: aprocessor or a micro-processor and adequate software and memory forstoring of the software, a Programmable Logic Device (PLD) or otherelectronic component(s) or processing circuitry configured to performthe actions described above, and illustrated, e.g., in FIG. 2.

FIG. 5 is a block diagram of a terminal device 500 according to yetanother embodiment of the present disclosure. The terminal device 500(referred to as “the first terminal device”) is in direct communicationwith a second terminal device.

The terminal device 500 includes a transceiver 510, a processor 520 anda memory 530. The memory 530 contains instructions executable by theprocessor 520 whereby the terminal device 500 is operative to performthe actions, e.g., of the procedure described earlier in conjunctionwith FIG. 1. Particularly, the memory 530 contains instructionsexecutable by the processor 520 whereby the terminal device 500 isoperative to: transmit to the second terminal device an MCS index, basedon which the second terminal device can obtain a modulation order and aTBS in accordance with a first mapping or a second mapping between MCSindices on one hand and modulation orders and TBSs on the other. The MCSindex is determined by the first terminal device by selectively applyingthe first or second mapping.

In an embodiment, the second mapping supports a higher modulation orderthan those supported by the first mapping.

In an embodiment, the first and second mappings have an overlappedportion.

In an embodiment, the overlapped portion is associated with one or moreof modulation orders supported by both the first and second mappings.

In an embodiment, the overlapped portion is associated with coding ratesbelow a predefined threshold.

In an embodiment, in a portion of the second mapping that does notoverlap the first mapping, each TBS associated with the second mappingis scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements,REs, available for data transmission.

In an embodiment, the MCS index is determined by the first terminaldevice by applying the first mapping when retransmission is configured,or the second mapping when no retransmission is configured and amodulation order and a TBS obtained by applying the first mapping wouldresult in a coding rate higher than a predefined threshold.

In an embodiment, the memory 530 further contains instructionsexecutable by the processor 520 whereby the terminal device 500 isoperative to transmit to the second terminal device an indicatorindicating which of the first and second mappings is applied by thefirst terminal device.

In an embodiment, the second terminal device supports the first mappingonly.

In an embodiment, the first and second terminal devices arecommunicating directly with each other on a sidelink for vehicularservices.

Additionally or alternatively, the memory 530 contains instructionsexecutable by the processor 520 whereby the terminal device 500 isoperative to perform the actions, e.g., of the procedure describedearlier in conjunction with FIG. 2. Particularly, the memory 530contains instructions executable by the processor 520 whereby theterminal device 500 is operative to: receive from the second terminaldevice an MCS index determined by the second terminal device by applyinga first mapping or a second mapping between MCS indices on one hand andmodulation orders and TBSs on the other; and obtain, based on the MCSindex, a modulation order and a TBS selectively in accordance with thefirst or second mapping.

In an embodiment, the second mapping supports a higher modulation orderthan those supported by the first mapping.

In an embodiment, the first and second mappings have an overlappedportion.

In an embodiment, the overlapped portion is associated with one or moreof modulation orders supported by both the first and second mappings.

In an embodiment, the overlapped portion is associated with coding ratesbelow a predefined threshold.

In an embodiment, in a portion of the second mapping that does notoverlap the first mapping, each TBS associated with the second mappingis scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements,REs, available for data transmission.

In an embodiment, the modulation order and the TBS are obtained by thefirst terminal device selectively in accordance with the first mappingwhen retransmission is configured, or with the second mapping when noretransmission is configured and a modulation order and a TBS obtainedin accordance with the first mapping would result in a coding ratehigher than a predefined threshold.

In an embodiment, the memory 530 further contains instructionsexecutable by the processor 520 whereby the terminal device 500 isoperative to receive from the second terminal device an indicatorindicating which of the first and second mappings is applied by thesecond terminal device.

In an embodiment, the second terminal device supports the first mappingonly.

In an embodiment, the first and second terminal devices arecommunicating directly with each other on a sidelink for vehicularservices.

The present disclosure also provides at least one computer programproduct in the form of a non-volatile or volatile memory, e.g., anon-transitory computer readable storage medium, an ElectricallyErasable Programmable Read-Only Memory (EEPROM), a flash memory and ahard drive. The computer program product includes a computer program.The computer program includes: code/computer readable instructions,which when executed by the processor 520 causes the terminal device 500to perform the actions, e.g., of the procedure described earlier inconjunction with FIG. 1 or 2.

The computer program product may be configured as a computer programcode structured in computer program modules. The computer programmodules could essentially perform the actions of the flow illustrated inFIG. 1 or 2.

The processor may be a single CPU (Central processing unit), but couldalso comprise two or more processing units. For example, the processormay include general purpose microprocessors; instruction set processorsand/or related chips sets and/or special purpose microprocessors such asApplication Specific Integrated Circuit (ASICs). The processor may alsocomprise board memory for caching purposes. The computer program may becarried by a computer program product connected to the processor. Thecomputer program product may comprise a non-transitory computer readablestorage medium on which the computer program is stored. For example, thecomputer program product may be a flash memory, a Random-access memory(RAM), a Read-Only Memory (ROM), or an EEPROM, and the computer programmodules described above could in alternative embodiments be distributedon different computer program products in the form of memories.

The disclosure has been described above with reference to embodimentsthereof. It should be understood that various modifications,alternations and additions can be made by those skilled in the artwithout departing from the spirits and scope of the disclosure.Therefore, the scope of the disclosure is not limited to the aboveparticular embodiments but only defined by the claims as attached.

What is claimed is:
 1. A method in a first terminal device forfacilitating direct communication with a second terminal device,comprising: transmitting to the second terminal device a Modulation andCoding Scheme (MCS) index, wherein based on the MCS index, the secondterminal device can obtain a corresponding modulation order and aTransport Block Size (TBS) in accordance with a first mapping or asecond mapping of modulation orders and TBSs, and wherein the secondmapping supports a higher modulation order than modulation orderssupported by the first mapping for some of same MCS indices; wherein theMCS index is determined by the first terminal device by selectiveapplication of use of the first mapping or the second mapping forcommunicating with the second terminal device.
 2. The method of claim 1,wherein the first and second mappings have an overlapped portion.
 3. Themethod of claim 2, wherein the overlapped portion is associated with oneor more of modulation orders supported by both the first and secondmappings.
 4. The method of claim 2, wherein the overlapped portion isassociated with coding rates below a predefined threshold.
 5. The methodof claim 4, wherein, in a portion of the second mapping that does notoverlap the first mapping, each TBS associated with the second mappingis scaled down with respect to a corresponding TBS associated with thefirst mapping by a factor dependent on a number of Resource Elements(REs) available for data transmission.
 6. The method of claim 1, whereinthe MCS index is determined by the first terminal device by applying thefirst mapping when retransmission is configured, or the second mappingwhen no retransmission is configured and a modulation order and a TBSobtained by applying the first mapping would result in a coding ratehigher than a predefined threshold.
 7. The method of claim 1, furthercomprising: transmitting to the second terminal device an indicatorindicating which of the first and second mappings is applied by thefirst terminal device.
 8. The method of claim 1, wherein the secondterminal device supports the first mapping only.
 9. The method of claim1, wherein the first and second terminal devices are communicatingdirectly with each other on a sidelink for vehicular services.
 10. Amethod in a first terminal device for facilitating direct communicationwith a second terminal device, comprising: receiving from the secondterminal device a Modulation and Coding Scheme (MCS) index transmittedby the second terminal device, wherein based on the MCS index, the firstterminal device can obtain a corresponding modulation order and aTransport Block Size (TBS) in accordance with a first mapping or asecond mapping of modulation orders and TBSs, and wherein the secondmapping supports a higher modulation order than modulation orderssupported by the first mapping for some of same MCS indices, in whichthe second terminal device determines the MCS index by selectiveapplication of use of the first mapping or the second mapping forcommunicating with the first terminal device; and obtaining, based onthe MCS index, a modulation order and a TBS in accordance with the firstmapping or the second mapping.
 11. The method of claim 10, wherein thefirst and second mappings have an overlapped portion.
 12. The method ofclaim 11, wherein the overlapped portion is associated with one or moreof modulation orders supported by both the first and second mappings.13. The method of claim 11, wherein the overlapped portion is associatedwith coding rates below a predefined threshold.
 14. The method of claim13, wherein, in a portion of the second mapping that does not overlapthe first mapping, each TBS associated with the second mapping is scaleddown with respect to a corresponding TBS associated with the firstmapping by a factor dependent on a number of Resource Elements (REs)available for data transmission.
 15. The method of claim 10, wherein themodulation order and the TBS are obtained by the first terminal devicein accordance with the first mapping when retransmission is configured,or with the second mapping when no retransmission is configured and amodulation order and a TBS obtained in accordance with the first mappingwould result in a coding rate higher than a predefined threshold. 16.The method of claim 10, further comprising: receiving from the secondterminal device an indicator indicating which of the first and secondmappings is applied by the second terminal device.
 17. The method ofclaim 10, wherein the first terminal device supports the first mappingonly.
 18. The method of claim 10, wherein the first and second terminaldevices are communicating directly with each other on a sidelink forvehicular services.
 19. A terminal device in direct communication with asecond terminal device, the terminal device comprising: a processor; anda memory, the memory comprising instructions which, when executed by theprocessor, cause the terminal device to: transmit to the second terminaldevice a Modulation and Coding Scheme (MCS) index, wherein based on theMCS index, the second terminal device can obtain a correspondingmodulation order and a Transport Block Size (TBS) in accordance with afirst mapping or a second mapping of modulation orders and TBSs, andwherein the second mapping supports a higher modulation order thanmodulation orders supported by the first mapping for some of same MCSindices; wherein the MCS index is determined by the terminal device byselective application of use of the first mapping or the second mappingfor communicating with the second terminal device.
 20. A terminal devicein direct communication with a second terminal device, the terminaldevice comprising: a processor; and a memory, the memory comprisinginstructions which, when executed by the processor, cause the terminaldevice to: receive from the second terminal device a Modulation andCoding Scheme (MCS) index transmitted by the second terminal device,wherein based on the MCS index, the terminal device can obtain acorresponding modulation order and a Transport Block Size (TBS) inaccordance with a first mapping or a second mapping of modulation ordersand TBSs, and wherein the second mapping supports a higher modulationorder than modulation orders supported by the first mapping for some ofsame MCS indices, in which the second terminal device determines the MCSindex by selective application of use of the first mapping or the secondmapping for communicating with the terminal device; and obtain, based onthe MCS index, a modulation order and a TBS in accordance with the firstmapping or the second mapping.